Drilling fluid and method for drilling a wellbore

Abstract

A method for drilling a wellbore into a formation uses a mixed metal-viscosified drilling fluid including at least 1% potassium salt and / or at least 0.05% calcium sulfate; circulating the drilling fluid through the well; and drilling into a formation. An anionic thinner may be added if the clay concentration of the drilling fluid reaches a problematic level to adversely affect pumpability of the fluid.

Description

FIELD[0001]This invention relates to methods and fluids used for drilling wells.BACKGROUND[0002]The process of drilling a hole in the ground for the extraction of a natural resource requires a fluid for removing the cuttings from the wellbore, lubricating and cooling the drill bit, controlling formation pressures and maintaining hole stability.[0003]Many formations present difficulties for drilling, as the formation materials which the drilling fluid contacts, can adversely affect the properties of the drilling fluid.[0004]For example, a fluid that minimizes formation damage and reduces whole mud loss by limiting invasion into the formation and permits easy flow back has been developed, termed herein the mixed metal-viscosified drilling fluids including mixed metal oxide (MMO), mixed metal hydroxide (MMH) and combinations of mixed metal oxide and hydroxide (MMOH). The mixed metal-viscosified drilling fluids contain a mixed metal viscosifier, which is an inorganic particle based on m...

AI Technical Summary

Benefits of technology

The addition of potassium salt and calcium sulfate stabilizes the drilling fluid's rheology, preventing fluid thinning and uncontrollable viscosity, allowing successful drilling through coal and clay zones while maintaining effective hole cleaning and minimizing fluid loss.

Problems solved by technology

Many formations present difficulties for drilling, as the formation materials which the drilling fluid contacts, can adversely affect the properties of the drilling fluid.

Unfortunately, however, the rheology of mixed metal-viscosified drilling fluids has broken down when coming into contact with coal fines generated from drilling into coal seams, especially young coal.

When the drilling fluid comes in contact with coal fines generated by drilling through the seams, the fluid thins, moving toward the rheology of water and therefore loses many of its beneficial properties.

Since coal seams are, in fact, often considered loss zone formations, and are weak and friable, the unsuitability of mixed metal-viscosified drilling fluids for drilling in coal containing formations is particularly problematic.

In addition to the well known sensitivity of mixed metal-viscosified drilling fluids to anionic compounds such as coal, these systems are also sensitive to the incorporation of reactive drilled clays in so far as such incorporated clays increase the viscosity of the fluid to uncontrollable levels and render the system unsuitable.